In a non-continuous magnetic tape system, magnetic tape is wound around one reel and retrieved from another reel. This arrangement can be present in traditional reel-to-reel systems, two-reel cartridge systems and single reel cartridge systems. In the case of non-continuous single cartridge systems, tape is wound to a take-up reel which is separate from the cartridge, and is usually a part of a tape transport mechanism.
"Tape recorder" is intended to mean magnetic tape transcription equipment. This includes standard tape recorders with fixed heads, as well as helical scan tape transcription equipment used in analog and digital tape recorders. In the preferred embodiment, digital transcription using linear transcription is, although the invention has application in other tape recording environments, such as helical and arcuate scanning. The invention is not intended to be limited to a particular use for the data. "Transcription" is intended to mean read and/or write operations of the tape recorder, and is not intended to be limited to a particular use for the data.
In using the terminology, it must be noted that tape is normally moved in both a forward and reverse direction between the supply and take-up reels. If the respective supply and take-up reels retain their designations, in reverse or rewind operation, tape is being taken up by the supply reel and supplied by the take-up reel. For the purposes of this description, the reel which at a given time is discharging tape will be referred to as the "unwinding reel," and the reel which at any given time is receiving tape will be referred to as the "winding reel. Tape fed to or from a reel normally meets the reel tangentially. Therefore, a location between the tape being fed and the reel can be referred to as, "inside the tape path," with respect to the reel and a location on the far side of the tape being fed would be, "outside the tape path," with respect to the reel. The tape on the reel is referred to as a, "tape pack."
Tape wound around a reel must be properly packed in order to achieve proper performance and to reduce tape damage. It has been found that tape packing, for a given tape configuration is a function of tape winding speed. Tape winding speed, as it affects tape packing is both rotational speed and linear speed. Linear speed, in particular seems to have a significant effect on causing air entrainment. Air entrainment occurs as a result of a tape floating force, which increases with tape travel speed, suggesting a mechanism similar to an active pressure air bearing. Irregular winding results from air entrainment, and is more likely to occur at high winding speeds. High winding speeds refer to a winding speed achieved on a particular tape transport mechanism that is above that needed for transcription, and usually limited by the ability of the tape transport mechanism to reliably transport the tape to a winding reel without damaging the tape. More importantly for this invention, the high speed operation is further limited by a desire not to cause air entrainment in the tape pack. Therefore, what may be a high speed for one tape transport mechanism may be much lower than either the rotational or linear speed of another tape transport mechanism. It is a purpose of the present invention to increase this speed for a given tape transport mechanism.
It is possible to reduce air entrainment by increasing tape tension. The ability to increase tension is dependent on the ability of the tape to receive tensile force without stretching or otherwise distorting. Usually tension is a predetermined factor, depending on an anticipated minimum strength of the tape and other drive performance factors. Thus, the ability to reduce air entrainment by increasing tension is limited. One prior art technique for tape winding included the use of a vacuum pump to reduce air pressure during tape transport operations.
In the case of magnetic tape used to store digital computer data, it is often desired to quickly wind the tape in order to position a desired location of the tape for transcription. This is necessitated by the nature of the media; that is, a web. Data location on the web is dependent on winding and unwinding operations. After the tape is wound to a desired location, the tape is read or written according to the operational protocols of the equipment, until it is necessary to perform read or write operations at a different location. Because of the need to change locations on the tape, the maximum speed that the tape can be wound becomes important to the speed of operation of the tape transcription equipment.
In addition, in some installations, the tape must be rewound as a routine matter, for example when it is necessary to change tape. This is particularly the case of single reel cartridges in non-continuous tape systems. In general, it is common to have operating requirements where it is desired to position tapes at a selected position. During such movement, performance is heavily dependent on tape transport speed.
It is desired to provide quality tape packing in that adjacent layers of tape on a reel are in good alignment. It is therefore desired to provide an ability to reduce air entrainment during winding, and ability to increase tape transport speed without substantially increasing air entrainment. Such an ability implies a requirement to reduce air entrainment for a given tape transport speed and tension. It would further be desired to reduce air entrainment without the use of a vacuum pump or as a supplement to the use of external negative pressure.